The conventionally known fuel injection devices include, for example, those described in Patent Literatures 1 and 2. The fuel injection device described in Patent Literature 1 shifts a fuel injection mode between a diffusion combustion mode and a premixed combustion mode according to engine loads. When this fuel injection device shifts the fuel injection mode from the diffusion combustion mode to the premixed combustion mode, it gradually decreases a fuel injection quantity (quantity of injected fuel) of main injection while gradually increasing a fuel injection quantity of pilot injection, with gradual decrease in oxygen concentration in a combustion chamber, and gradually narrows the interval between pilot injection and main injection.
The fuel injection device described in Patent Literature 2 injects fuel contributing to combustion, in two separate injections. At this time, the first time injection is carried out at timing to enable premixed combustion and the second time injection is carried out at timing to enable premixed combustion and before the compression top dead center (TDC). Furthermore, the timing of the first time injection is advanced with increase in engine load to expand the interval between the first time injection and the second time injection.